Spectral emission modification using localized surface plasmon of metallic nanoparticles

ABSTRACT

A method for engineering a line shape of emission spectrum of an organic emissive material in an electroluminescent device is disclosed in which a layer of plasmonic metallic nanostructures having a localized surface plasmonic resonance (LSPR) is provided in proximity to the emissive layer and the layer of plasmonic metallic nanostructures is greater than 2 nm but less than 100 nm from the emissive layer and the LSPR of the plasmonic metallic nanostructures matches the emission wavelength of the organic emissive material. An electroluminescent device incorporating the plasmonic metallic nanostructures is also disclosed.

JOINT RESEARCH AGREEMENT

The claimed invention was made by, on behalf of, and/or in connectionwith the following parties to a joint university corporation researchagreement: University of Pennsylvania and Universal Display Corporation.The agreement was in effect on and before the date the claimed inventionwas made, and the claimed invention was made as a result of activitiesundertaken within the scope of the agreement.

FIELD OF THE INVENTION

The present invention relates generally to organic light emittingdevices.

BACKGROUND

Opto-electronic devices that make use of organic materials are becomingincreasingly desirable for a number of reasons. Many of the materialsused to make such devices are relatively inexpensive, so organicopto-electronic devices have the potential for cost advantages overinorganic devices. In addition, the inherent properties of organicmaterials, such as their flexibility, may make them well suited forparticular applications such as fabrication on a flexible substrate.Examples of organic opto-electronic devices include organic lightemitting devices (OLEDs), organic phototransistors, organic photovoltaiccells, and organic photodetectors. For OLEDs, the organic materials mayhave performance advantages over conventional materials. For example,the wavelength at which an organic emissive layer emits light maygenerally be readily tuned with appropriate dopants.

OLEDs make use of thin organic films that emit light when voltage isapplied across the device. OLEDs are becoming an increasinglyinteresting technology for use in applications such as flat paneldisplays, illumination, and backlighting. Several OLED materials andconfigurations are described in U.S. Pat. Nos. 5,844,363, 6,303,238, and5,707,745, which are incorporated herein by reference in their entirety.

One application for phosphorescent emissive molecules is a full colordisplay. Industry standards for such a display call for pixels adaptedto emit particular colors, referred to as “saturated” colors. Inparticular, these standards call for saturated red, green, and bluepixels. Color may be measured using CIE coordinates, which are wellknown to the art.

One example of a green emissive molecule is tris(2-phenylpyridine)iridium, denoted Ir(ppy)₃, which has the following structure:

In this, and later figures herein, we depict the dative bond fromnitrogen to metal (here, Ir) as a straight line.

As used herein, the term “organic” includes polymeric materials as wellas small molecule organic materials that may be used to fabricateorganic opto-electronic devices. “Small molecule” refers to any organicmaterial that is not a polymer, and “small molecules” may actually bequite large. Small molecules may include repeat units in somecircumstances. For example, using a long chain alkyl group as asubstituent does not remove a molecule from the “small molecule” class.Small molecules may also be incorporated into polymers, for example as apendent group on a polymer backbone or as a part of the backbone. Smallmolecules may also serve as the core moiety of a dendrimer, whichconsists of a series of chemical shells built on the core moiety. Thecore moiety of a dendrimer may be a fluorescent or phosphorescent smallmolecule emitter. A dendrimer may be a “small molecule,” and it isbelieved that all dendrimers currently used in the field of OLEDs aresmall molecules.

As used herein, “top” means furthest away from the substrate, while“bottom” means closest to the substrate. Where a first layer isdescribed as “disposed over” a second layer, the first layer is disposedfurther away from substrate. There may be other layers between the firstand second layer, unless it is specified that the first layer is “incontact with” the second layer. For example, a cathode may be describedas “disposed over” an anode, even though there are various organiclayers in between.

As used herein, “solution processible” means capable of being dissolved,dispersed, or transported in and/or deposited from a liquid medium,either in solution or suspension form.

A ligand may be referred to as “photoactive” when it is believed thatthe ligand directly contributes to the photoactive properties of anemissive material. A ligand may be referred to as “ancillary” when it isbelieved that the ligand does not contribute to the photoactiveproperties of an emissive material, although an ancillary ligand mayalter the properties of a photoactive ligand.

As used herein, and as would be generally understood by one skilled inthe art, a first “Highest Occupied Molecular Orbital” (HOMO) or “LowestUnoccupied Molecular Orbital” (LUMO) energy level is “greater than” or“higher than” a second HOMO or LUMO energy level if the first energylevel is closer to the vacuum energy level. Since ionization potentials(IP) are measured as a negative energy relative to a vacuum level, ahigher HOMO energy level corresponds to an IP having a smaller absolutevalue (an IP that is less negative). Similarly, a higher LUMO energylevel corresponds to an electron affinity (EA) having a smaller absolutevalue (an EA that is less negative). On a conventional energy leveldiagram, with the vacuum level at the top, the LUMO energy level of amaterial is higher than the HOMO energy level of the same material. A“higher” HOMO or LUMO energy level appears closer to the top of such adiagram than a “lower” HOMO or LUMO energy level.

As used herein, and as would be generally understood by one skilled inthe art, a first work function is “greater than” or “higher than” asecond work function if the first work function has a higher absolutevalue. Because work functions are generally measured as negative numbersrelative to vacuum level, this means that a “higher” work function ismore negative. On a conventional energy level diagram, with the vacuumlevel at the top, a “higher” work function is illustrated as furtheraway from the vacuum level in the downward direction. Thus, thedefinitions of HOMO and LUMO energy levels follow a different conventionthan work functions.

More details on OLEDs, and the definitions described above, can be foundin U.S. Pat. No. 7,279,704, which is incorporated herein by reference inits entirety.

SUMMARY OF THE INVENTION

According to an aspect of the present disclosure, a method forengineering a line shape of emission spectrum of an organic emissivematerial in an electroluminescent device is disclosed, wherein theelectroluminescent device comprises an anode layer, a cathode layer, andan emissive layer disposed in between the anode and the cathode layers,wherein an organic emissive material is provided in the emissive layer.The method comprises: providing a layer of plasmonic metallicnanostructures having a localized surface plasmonic resonance (LSPR) inproximity to the emissive layer, wherein the layer of plasmonic metallicnanostructures is greater than 2 nm from but less than 100 nm from theemissive layer, and the LSPR of the layer of plasmonic metallicnanostructures is within ±10 nm of the peak emission wavelength of theorganic emissive material and more preferably within ±5 nm of the peakemission wavelength of the organic emissive material.

According to another aspect of the present disclosure, anelectroluminescent device comprising an anode layer, a cathode layer,and a stack of layers disposed between the anode layer and the cathodelayer is disclosed. The stack of layers includes an emissive layer and afirst layer of plasmonic metal nanostructures. The emissive layerincludes an organic emissive material having an emission wavelength, andthe first layer of plasmonic metal nanostructures has a LSPR, whereinthe layer of plasmonic metal nanostructures is great than 2 nm from butless than 100 nm from the emissive layer and the LSPR of the layer ofplasmonic metal nanostructures is within ±10 nm of the peak emissionwavelength of the organic emissive material and more preferably within±5 nm of the peak emission wavelength of the organic emissive material.

According to some embodiments, an electroluminescent device comprisingan anode layer, a cathode layer, and a stack of layers disposed betweenthe anode layer and the cathode layer is disclosed. The stack of layerscomprises: an emissive layer comprising an organic emissive material,the organic emissive material having an emission wavelength; a holetransporting layer disposed between the emissive layer and the anodelayer; and an electron transporting layer disposed between the emissivelayer and the cathode, wherein the anode layer or the cathode layer is alayer of plasmonic metal nanostructures having a LSPR, wherein the layerof plasmonic metal nanostructures is greater than 2 nm from but lessthan 100 nm from the emissive layer and the LSPR of the layer ofplasmonic metal nanostructures is within ±10 nm of the peak emissionwavelength of the organic emissive material and more preferably within±5 nm of the peak emission wavelength of the organic emissive material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an organic light emitting device.

FIG. 2 shows an inverted organic light emitting device that does nothave a separate electron transport layer.

FIG. 3A is a normalized plot showing the extinction spectrum of the LSPRof 5 nm Ag nanoparticle films of different thicknesses.

FIG. 3B shows emission spectrum of blue organometallic phosphor place inproximity to the Ag nanoparticle films of FIG. 3A.

FIG. 4 illustrates this schematically for a hypothetical organometallicphosphor

FIG. 5 is a plot of the extinction spectrum of Ag nanostructures as afunction of nanostructure size.

FIG. 6 is a top down view of an example of a 2 dimensional pattern of apatterned plasmonic metallic film.

DETAILED DESCRIPTION

Generally, an OLED comprises at least one organic layer disposed betweenand electrically connected to an anode and a cathode. When a current isapplied, the anode injects holes and the cathode injects electrons intothe organic layer(s). The injected holes and electrons each migratetoward the oppositely charged electrode. When an electron and holelocalize on the same molecule, an “exciton,” which is a localizedelectron-hole pair having an excited energy state, is formed. Light isemitted when the exciton relaxes via a photoemissive mechanism. In somecases, the exciton may be localized on an excimer or an exciplex.Non-radiative mechanisms, such as thermal relaxation, may also occur,but are generally considered undesirable.

The initial OLEDs used emissive molecules that emitted light from theirsinglet states (“fluorescence”) as disclosed, for example, in U.S. Pat.No. 4,769,292, which is incorporated by reference in its entirety.Fluorescent emission generally occurs in a time frame of less than 10nanoseconds.

More recently, OLEDs having emissive materials that emit light fromtriplet states (“phosphorescence”) have been demonstrated. Baldo et al.,“Highly Efficient Phosphorescent Emission from OrganicElectroluminescent Devices,” Nature, vol. 395, 151-154,1998; (“Baldo-I”)and Baldo et al., “Very high-efficiency green organic light-emittingdevices based on electrophosphorescence,” Appl. Phys. Lett., vol. 75,No. 3, 4-6 (1999) (“Baldo-II”), which are incorporated by reference intheir entireties. Phosphorescence is described in more detail in U.S.Pat. No. 7,279,704 at cols. 5-6, which are incorporated by reference.

FIG. 1 shows an organic light emitting device 100. The figures are notnecessarily drawn to scale. Device 100 may include a substrate 110, ananode 115, a hole injection layer 120, a hole transport layer 125, anelectron blocking layer 130, an emissive layer 135, a hole blockinglayer 140, an electron transport layer 145, an electron injection layer150, a protective layer 155, and a cathode 160, and a barrier layer 170.Cathode 160 is a compound cathode having a first conductive layer 162and a second conductive layer 164. Device 100 may be fabricated bydepositing the layers described, in order. The properties and functionsof these various layers, as well as example materials, are described inmore detail in U.S. Pat. No. 7,279,704 at cols. 6-10, which areincorporated by reference.

More examples for each of these layers are available. For example, aflexible and transparent substrate-anode combination is disclosed inU.S. Pat. No. 5,844,363, which is incorporated by reference in itsentirety. An example of a p-doped hole transport layer is m-MTDATA dopedwith F4-TCNQ at a molar ratio of 50:1, as disclosed in U.S. PatentApplication Publication No. 2003/0230980, which is incorporated byreference in its entirety. Examples of emissive and host materials aredisclosed in U.S. Pat. No. 6,303,238 to Thompson et al., which isincorporated by reference in its entirety. An example of an n-dopedelectron transport layer is BPhen doped with Li at a molar ratio of 1:1,as disclosed in U.S. Patent Application Publication No. 2003/0230980,which is incorporated by reference in its entirety. U.S. Pat. Nos.5,703,436 and 5,707,745, which are incorporated by reference in theirentireties, disclose examples of cathodes including compound cathodeshaving a thin layer of metal such as Mg:Ag with an overlyingtransparent, electrically-conductive, sputter-deposited ITO layer. Thetheory and use of blocking layers is described in more detail in U.S.Pat. No. 6,097,147 and U.S. Patent Application Publication No.2003/0230980, which are incorporated by reference in their entireties.Examples of injection layers are provided in U.S. Patent ApplicationPublication No. 2004/0174116, which is incorporated by reference in itsentirety. A description of protective layers may be found in U.S. PatentApplication Publication No. 2004/0174116, which is incorporated byreference in its entirety.

FIG. 2 shows an inverted OLED 200. The device includes a substrate 210,a cathode 215, an emissive layer 220, a hole transport layer 225, and ananode 230. Device 200 may be fabricated by depositing the layersdescribed, in order. Because the most common OLED configuration has acathode disposed over the anode, and device 200 has cathode 215 disposedunder anode 230, device 200 may be referred to as an “inverted” OLED.Materials similar to those described with respect to device 100 may beused in the corresponding layers of device 200. FIG. 2 provides oneexample of how some layers may be omitted from the structure of device100.

The simple layered structure illustrated in FIGS. 1 and 2 is provided byway of non-limiting example, and it is understood that embodiments ofthe invention may be used in connection with a wide variety of otherstructures. The specific materials and structures described areexemplary in nature, and other materials and structures may be used.Functional OLEDs may be achieved by combining the various layersdescribed in different ways, or layers may be omitted entirely, based ondesign, performance, and cost factors. Other layers not specificallydescribed may also be included. Materials other than those specificallydescribed may be used. Although many of the examples provided hereindescribe various layers as comprising a single material, it isunderstood that combinations of materials, such as a mixture of host anddopant, or more generally a mixture, may be used. Also, the layers mayhave various sublayers. The names given to the various layers herein arenot intended to be strictly limiting. For example, in device 200, holetransport layer 225 transports holes and injects holes into emissivelayer 220, and may be described as a hole transport layer or a holeinjection layer. In one embodiment, an OLED may be described as havingan “organic layer” disposed between a cathode and an anode. This organiclayer may comprise a single layer, or may further comprise multiplelayers of different organic materials as described, for example, withrespect to FIGS. 1 and 2.

Structures and materials not specifically described may also be used,such as OLEDs comprised of polymeric materials (PLEDs) such as disclosedin U.S. Pat. No. 5,247,190 to Friend et al., which is incorporated byreference in its entirety. By way of further example, OLEDs having asingle organic layer may be used. OLEDs may be stacked, for example asdescribed in U.S. Pat. No. 5,707,745 to Forrest et al, which isincorporated by reference in its entirety. The OLED structure maydeviate from the simple layered structure illustrated in FIGS. 1 and 2.For example, the substrate may include an angled reflective surface toimprove outcoupling, such as a mesa structure as described in U.S. Pat.No. 6,091,195 to Forrest et al., and/or a pit structure as described inU.S. Pat. No. 5,834,893 to Bulovic et al., which are incorporated byreference in their entireties.

Unless otherwise specified, any of the layers of the various embodimentsmay be deposited by any suitable method. For the organic layers,preferred methods include thermal evaporation, ink-jet, such asdescribed in U.S. Pat. Nos. 6,013,982 and 6,087,196, which areincorporated by reference in their entireties, organic vapor phasedeposition (OVPD), such as described in U.S. Pat. No. 6,337,102 toForrest et al., which is incorporated by reference in its entirety, anddeposition by organic vapor jet printing (OVJP), such as described inU.S. patent application Ser. No. 10/233,470, which is incorporated byreference in its entirety. Other suitable deposition methods includespin coating and other solution based processes. Solution basedprocesses are preferably carried out in nitrogen or an inert atmosphere.For the other layers, preferred methods include thermal evaporation.Preferred patterning methods include deposition through a mask, coldwelding such as described in U.S. Pat. Nos. 6,294,398 and 6,468,819,which are incorporated by reference in their entireties, and patterningassociated with some of the deposition methods such as ink-jet and OVJD.Other methods may also be used. The materials to be deposited may bemodified to make them compatible with a particular deposition method.For example, substituents such as alkyl and aryl groups, branched orunbranched, and preferably containing at least 3 carbons, may be used insmall molecules to enhance their ability to undergo solution processing.Substituents having 20 carbons or more may be used, and 3-20 carbons isa preferred range. Materials with asymmetric structures may have bettersolution processibility than those having symmetric structures, becauseasymmetric materials may have a lower tendency to recrystallize.Dendrimer substituents may be used to enhance the ability of smallmolecules to undergo solution processing.

Devices fabricated in accordance with embodiments of the invention maybe incorporated into a wide variety of consumer products, including flatpanel displays, computer monitors, medical monitors, televisions,billboards, lights for interior or exterior illumination and/orsignaling, heads up displays, fully transparent displays, flexibledisplays, laser printers, telephones, cell phones, personal digitalassistants (PDAs), laptop computers, digital cameras, camcorders,viewfinders, micro-displays, vehicles, a large area wall, theater orstadium screen, or a sign. Various control mechanisms may be used tocontrol devices fabricated in accordance with the present invention,including passive matrix and active matrix. Many of the devices areintended for use in a temperature range comfortable to humans, such as18 degrees C. to 30 degrees C., and more preferably at room temperature(20-25 degrees C.).

The materials and structures described herein may have applications indevices other than OLEDs. For example, other optoelectronic devices suchas organic solar cells and organic photodetectors may employ thematerials and structures. More generally, organic devices, such asorganic transistors, may employ the materials and structures.

The terms halo, halogen, alkyl, cycloalkyl, alkenyl, alkynyl, arylkyl,heterocyclic group, aryl, aromatic group, and heteroaryl are known tothe art, and are also defined in U.S. Pat. No. 7,279,704 at cols. 31-32,which are incorporated herein by reference.

The emission spectrum line shape and spectral width of emission areintrinsic properties of the chemical composition of organic dyes. Foroptoelectronic devices such as OLEDs, modification of the intrinsicemission spectrum through device engineering rather than chemistry isadvantageous to increase color saturation, color rendering index, andefficiency. The conventional way of modifying or tuning emissionspectrum line shape by device engineering is by introducing an opticalcavity. This, however, creates trade-offs between the spectral lineshape, the direction of emission, and efficiency. Optical cavities aretypically narrow in bandwidth. Thus, there is a need for an improved wayof modifying the emission spectrum line shape by other avenues of deviceengineering.

The inventors have unexpectedly discovered that the line shape of theemission of organic emissive dopants in optoelectronic devices can bemodified or tuned using plasmonic metal nanostructures, in the form ofeither patterned metal films or colloidal nanoparticles. The plasmonicmetal nanostructures, when in proximity to emissive materials, canmodify the spectral line shape of emission. This find was unexpected asthe spectral line shape is assumed to be an inherent property of themolecule which cannot be modified. This is made possible through thecareful optimization of the localized surface plasmon resonance (LSPR)of the plasmonic metal nanostructures. We find a large line shapemodification when the wavelength of the maximum extinction (i.e.absorption and scattering) of the LSPR of the plasmonic metalnanostructure is within ±10 nm of the peak emission wavelength of theorganic emissive material and more preferably within ±5 nm of the peakemission wavelength of the organic emissive material. Further, inventorsbelieve that the plasmonic metal nanostructures can be used to modifythe peak wavelength of the emitter which previously is something onlythought possible through the use of an optical cavity.

The collective oscillations of electrons in the plasmonic metalnanostructures that are excited by light creates strong electric fieldsat energies characteristic of the plasmonic metal nanostructure LSPR.These strong electric fields alter the environment and therefore thequantum yield and emission rate of an organic dye (i.e. an emitter)placed in proximity to the plasmonic metal nanostructure. Incorporationof plasmonic metal nanostructures with the energy of LSPR tuned to aspecific value allows for independent tuning of emission spectrum lineshape, angular dependence, and polarization of emission of organic dyesin optoelectronic devices.

According to some embodiments, a method for engineering the line shapeof the emission spectrum of an organic emissive material in anelectroluminescent device is disclosed, wherein the electroluminescentdevice comprises an anode layer, a cathode layer, and an emissive layerdisposed in between the anode and the cathode layers, wherein an organicemissive material is provided in the emissive layer. The methodcomprises: providing a layer of plasmonic metallic nanostructures havinga LSPR in proximity to the emissive layer, wherein the layer ofplasmonic metallic nanostructures is greater than 2 nm from but lessthan 100 nm from the emissive layer and the LSPR of the layer ofplasmonic metallic nanostructures is within ±10 nm of the peak emissionwavelength of the organic emissive material and more preferably within±5 nm of the peak emission wavelength of the organic emissive material.

According to some embodiments, an improved electroluminescent deviceincorporating teachings of this disclosure is disclosed. Theelectroluminescent device comprises: an anode layer; a cathode layer:and a stack of layers disposed between the anode layer and the cathodelayer. The stack of layers include: an emissive layer comprising anorganic emissive material, the organic emissive material having anemission wavelength; and a first layer of plasmonic metal nanostructureshaving a localized surface plasmonic resonance (LSPR) disposed with thestack of layers, wherein the layer of plasmonic metal nanostructures isgreater than 2 nm from but less than 100 nm from the emissive layer andthe LSPR of the layer of plasmonic metal nanostructures is tuned to bewithin ±10 nm of the peak emission wavelength of the organic emissivematerial and more preferably within ±5 nm of the peak emissionwavelength of the organic emissive material.

The limits of greater than 2 nm but less than 100 nm from the emissivelayer for the metal nanostructures depend on both the size and thecomposition of the metal nanostructures. The 2 nm limit comes fromquenching of the luminescence of the emitter by energy transfer/chargetransfer to the metal nanoparticle. Technically, this does depend on thedensity of states of the metal, although inventors believe that this hasa weaker dependence on size and composition than the long length scalefor most systems that would be selected for this application. On thelonger side, the 100 nm limit does matter as not only the energy, butthe strength of the plasmon resonance and the associated field dependson size and composition of the metal nanostructures.

The optimal distance of the metal nanostructures from the emissive layerwithin the specified limits will depend on the composition and size ofthe metal nanostructures as these will affect the energy and strength ofthe plasmon resonance. The optimal distance of the metal nanostructuresfrom the emissive layer also depends on the thickness of the emissivelayer because the emitter dopant compounds are dispersed within theemissive layer. The optimal thickness for the emissive layer is lessthan or equal to 100 nm and preferably less than or equal to 50 nm.

The limits are encompassing to capture the length scales at which theenhancement would be active for a broad range of metal nanostructuresizes and compositions.

According to some embodiments of the electroluminescent device, thestack of layers comprises: a hole transporting layer (HTL) disposedbetween the emissive layer and the anode layer, and wherein the firstlayer of plasmonic metal nanostructures is disposed between the HTL andthe anode layer. According to some embodiments, the first layer ofplasmonic metal nanostructures has a thickness and comprises a pluralityof plasmonic metal nanostructures having a feature size and thethickness of the first layer of plasmonic metal nanostructures isselected to result in the LSPR of the first layer of plasmonic metalnanostructures to be within ±10 nm of the peak emission wavelength ofthe organic emissive material and more preferably within ±5 nm of thepeak emission wavelength of the organic emissive material.

According to some embodiments, the first layer of plasmonic metalnanostructures has a thickness and comprises a plurality of plasmonicmetal nanoparticles having a particle size, wherein the particle size ofthe plurality of plasmonic metal nanoparticles is selected to result inthe LSPR of the first layer of plasmonic metal nanoparticles be within±10 nm of the peak emission wavelength of the organic emissive materialand more preferably within ±5 nm of the peak emission wavelength of theorganic emissive material.

According to some embodiments, the stack of layers comprising anelectron transporting layer (ETL) disposed between the emissive layerand the cathode layer, wherein the first layer of plasmonic metalnanostructures is disposed between the ETL and the cathode layer.According to some embodiments, the first layer of plasmonic metalnanostructures has a thickness and comprises a plurality of plasmonicmetal nanostructures having a particle size and the thickness of thefirst layer of plasmonic metal nanostructures selected to result in theLSPR of the first layer of plasmonic metal nanostructures being within±10 nm of the peak emission wavelength of the organic emissive materialand more preferably within ±5 nm of the peak emission wavelength of theorganic emissive material.

According to some embodiments, the stack of layers further comprising ahole transport layer (HTL) disposed between the emissive layer and theanode layer, and wherein a second layer of plasmonic metalnanostructures is disposed between the HTL and the anode layer. In someembodiments, each of the first and second layers of plasmonic metalnanostructures has a thickness and comprises a plurality of plasmonicmetal nanostructures having a feature size and the thickness of each ofthe first and second layers of plasmonic metal nanostructures isselected to result in the LSPR of the first and second layers ofplasmonic metal nanostructures be within ±10 nm of the peak emissionwavelength of the organic emissive material and more preferably within±5 nm of the peak emission wavelength of the organic emissive material.

According to some embodiments, each of the first and second layers ofplasmonic metal nanostructures are a plurality of plasmonic metalnanoparticles having a particle size selected to result in the LSPR ofthe first and second layers of plasmonic metal nanoparticles be within±10 nm of the peak emission wavelength of the organic emissive materialand more preferably within ±5 nm of the peak emission wavelength of theorganic emissive material.

According to another aspect of the present disclosure, anelectroluminescent device comprising the following is disclosed:

an anode layer;

a cathode layer: and

a stack of layers disposed between the anode layer and the cathodelayer, said stack of layers including: an emissive layer comprising anorganic emissive material, the organic emissive material having anemission wavelength; a hole transporting layer disposed between theemissive layer and the anode layer; and an electron transporting layerdisposed between the emissive layer and the cathode; wherein the anodelayer or the cathode layer is a layer of plasmonic metal nanostructureshaving a localized surface plasmonic resonance (LSPR), wherein the layerof plasmonic metal nanostructures is greater than 2 nm from but lessthan 100 nm from the emissive layer and the LSPR of the layer ofplasmonic metal nanostructures is tuned to match the emission wavelengthof the organic emissive material.

In some embodiments of the electroluminescent device, the plasmonicmetal nanostructures are plasmonic metal nanoparticles, wherein theplasmonic metal nanoparticles have a particle size selected to result inthe LSPR of the layer of plasmonic metal nanoparticles match theemission wavelength of the organic emissive material.

The Plasmonic Metal Nanostructures

The plasmonic metal nanostructures may be fabricated by combining thephysical deposition of metal (e.g. through thermal or e-beam evaporationor sputtering) to form thin films with lithographic patterning of themetal to create the desired size and shape of the nanostructures.Alternatively, metal nanostructures may be synthesized throughwet-chemical methods (e.g. solvothermal synthesis). The plasmonic metalnanostructure is selected to operate preferably in the UV or visiblelight range and therefore is made of a high carrier density metal,preferably Al, Ag, or Au is desired. The feature size of the plasmonicnanostructures are sub-wavelength and therefore the feature size in therange of 2-400 nm, and preferably 5-200 nm are appropriate. The featuresize is the lateral dimensions for the lithographically definedstructures. For example, they can look like discs that may be 100s ofnanometers in diameter, but they would be thin having thickness of 10sof nanometers. The plasmonic nanostructures should not be much thickerbecause they would negatively affect the deposited organic layers. Thenanostructures can be made into any desired shape such as discs,spheres, rods, etc. using various fabrication methods known in the art.

The combination of metal nanostructure composition, size, and shape areselected to be resonant with the wavelengths of emission of the emittersused in the OLED (e.g. for a blue emitter, ˜100 nm diameter Al or ˜5 nmdiameter Ag nanoparticles are resonant with emission of the emitter,whereas for green and red emitters, larger Al or Ag and Aunanostructures are appropriate).

When designing the plasmonic metal nanostructure for visible wavelengthemitters, the choice of metal is selected by the strength of the plasmonin different spectral regions. The strength of the plasmon depends onthe real and imaginary parts of the metal dielectric function. Thus, forblue and green emitters one would typically use Al or Ag nanoparticlesas the plasmonic material. For red emitters one can also use Aunanoparticles or alloys of Ag and Au. In general, the higher the bulksurface plasmon resonance, the more negative the real part of thedielectric function, and therefore the larger the feature size of themetal plasmonic nanostructures that will generate the same wavelengthpeak LSPR. For example, when targeting a blue phosphorescent emitterwith peak wavelength between 440-490 nm, for Ag nanostructures thepreferred feature size is between 2 and 200 nm, more preferably between2 and 100 nm, most preferred between 2 and 50 nm. For Al nanostructures,the preferred feature size is between 2 and 500 nm. The advantage ofusing Al as the plasmonic metallic nanostructure is that as the featuresize of the nanostructures gets larger the efficiency of scattering alsoincreases. For the films of nanocrystals, as the size and thereforevolume fraction of the nanocrystals increase with respect the volumefraction of a matrix, the dielectric constant of the medium alsochanges. Therefore, the scattering efficiency and resonance wavelengthdepend on the size of the nanocrystals and the contrast in dielectricconstant between that of the nanocrystals and that of the surroundingmatrix.

The LSPR of the plasmonic nanostructures does depend on the material(based on their real and imaginary parts of the dielectric constants)and in the case of non-spherical nanostructures, the aspect ratio of thenanostructures, can affect the LSPR. The greater the aspect ratio thegreater the LSPR wavelength will be. For example, for disc-shaped metalfilm nanostructures, as the feature size of a disc increases for a giventhickness of the material, the greater its aspect ratio will be andtherefore its LSPR wavelength will increase. Same trend will be true forrod-shaped nanostructures. For example, when targeting a bluephosphorescent emitter with peak wavelength between 440-490 nm usingnon-spherical Al nanostructures having feature size between 2 and 500nm, the thickness of the Al nanostructures would preferably becontrolled to be less than 50 nm, which would provide the aspect ratioappropriate to control the wavelength. For plasmonic nanostructureshaving different shapes, the feature size and the thickness will need tobe adjusted to achieve the desired LSPR.

The peak of the extinction will shift to longer wavelengths when thefeature size of the nanostructure increases. Thus, to have a largefeature size plasmonic nanostructure that has a LSPR between 440-490 nmrequires a material with a very high energy bulk plasmonic resonancesuch as Al. The size of the nanostructure is also important for tuningthe LSPR to match the peak emission wavelength of the emitter.Typically, as the nanostructure feature size becomes smaller the LSPRshifts to shorter wavelength (higher energy). FIG. 5 shows a plot of theextinction spectrum of Ag nanostructures as a function of their featuresize. The Ag nanostructures are particles having diameters ranging from10 to 100 nm (each plot line is labeled with the corresponding diameter)at a mass concentration of 0.02 mg/mL provided by Sigma-Aldrich company.

The phenomena here are the result of the spectral alignment between aLSPR of the nanostructured metal and the emitter. A modification of theline shape of emission is not expected to occur for coupling between theemitter and a surface plasmon in bulk metals or smooth metal thin films.Here we use plasmonic metal nanostructures featuring free surfaces.Optical excitation causes the electrons in the metal to be “confined”and oscillate in the nanostructures creating the LSPR. This enablesspectral alignment between the emitter and the nanostructures leading toline shape engineering.

According to some embodiments, the plasmonic metal nanostructures can becolloidal nanoprticles. Colloidal nanoparticles will have a ligand whichadds solubility/dispersibility to the colloidal nanoparticles. Thechemical composition of the ligand can be tuned to providesolubility/dispersibility in a number of solvents including polar andnon-polar organic solvents and water.

According to some embodiments, the plasmonic metal nanostructures can bepatterned metallic films. When using a patterned metallic film, thefilms are patterned in 2-dimensions and the maximum feature size is asdefined above for the wavelength of the emitter and the metal beingused.

Preferably, such patterned plasmonic metallic film is at least one setof gratings formed of wavelength-sized or sub-wavelength-sized featuresthat are arranged periodically, quasi-periodically, or randomly, orsub-wavelength-sized features that are arranged periodically,quasi-periodically, or randomly. In one preferred embodiment, thewavelength-sized features and the sub-wavelength-sized features can havesharp edges.

The patterned plasmonic metallic film can be fabricated in a number ofways. The most precise methods include: photolithography, imprintlithography, or electron beam lithography. Quasiperiodicity may beachieved through depositing on, or templating the metallic film with, aself-assembled layer. The self-assembled layer can be self-assembledcolloidal nanoparticles or self-assembled polymer template followed bymetal deposition. Quasiperiodic or random patterning may be achievedthrough roughening the substrate of the OLED device to add texture tothe enhancement layer. Any of these methods may be used to pattern asolid metallic film to form a patterned plasmonic metallic film. Thepatterned plasmonic metallic film may either be patterned as part of theOLED fabricating process steps or the metallic film may be patterned onan alternative substrate and then place on the OLED device. Placementmethods can include stamping, wafer bonding, wet transfer printing, drytransfer printing, and ultrasonic bonding.

Periodically patterned metallic film may also be referred to asgratings. In a 2-dimensional grating, the structural features formingthe grating, the wavelength-sized or sub-wavelength-sized features, arearranged in a periodic pattern that is uniform along one direction(i.e., in x-direction or y-direction as labeled in FIG. 6) in the planeof the metallic film. The top-down view of FIG. 6 illustrates anexample. In FIG. 6, the dark regions and the white regions illustratethe two different materials forming the patterned metallic film. Asunderstood by those skilled in the art, either material (i.e., the darkregions or the white regions in the figures) can be considered to be thewavelength-sized or sub-wavelength-sized features forming the grating.

The patterned metallic film can be formed as at least one set ofgratings. In 2-dimensional patterned grating embodiments where one filmlayer has one grating pattern, the grating can have a periodic pattern,wherein the wavelength-sized or sub-wavelength-sized features arearranged uniformly along one direction. The wavelength-sized orsub-wavelength-sized features can be arranged with a pitch of 100-2000nm with a 10-90% duty cycle, and more preferably 20-1000 nm with a30-70% duty cycle. The pattern may be composed of lines or holes in themetallic film. However the pattern does not need to be symmetric. Itcould be locally patterned over the distance of 1 micrometer and thenhave no patterning for several micrometers before repeating the patternagain. By applying this asymmetric patterned metallic film to shape theemission of an emissive layer with multiple emitters, we can haveregions of the substrate which are patterned to change the spectral lineshape of one color emitter while other regions of the substrate can bepatterned to modify the spectral line shape of another color emitter.

In some embodiments of the electroluminescent device such as an OLED,the plasmonic metal nanostructure may be used at 1) the interfacebetween the transparent front electrode and the HTL or in place of thetransparent front electrode, 2) within the OLED stack of HTL, EML, orETL, or 3) at the interface between the ETL and the back cathode. Theplasmonic nanostructure should be placed in proximity to the emitter, toensure the electric field of the LSPR has a strong influence on theemitter, but not too close (e.g. typically greater than 2 nm orpreferably less than 5 nm, depending on the metal selected) to preventquenching. However the effect diminishes as a function of distancebetween the plasmonic metal nanostructure and the emitter. Thus thepreferred maximum distance for the plasmonic metal nanostructure fromthe emitter is 100 nm, more preferrably 75 nm, and most preferrably 50nm. Thus, in some embodiments, the layer of plasmonic metalnanostructure having a LSPR is to be disposed at a distance greater than2 nm but less than 100 nm from the emitter layer.

In addition to using the nanostructures for enhancing the electric fieldusing the LSPR, the plasmonic metal nanostructures also exhibit anegative value of the real component of the refractive index which iswavelength dependent. In the effective medium approximation the localdielectric constant can be considered to be the volume fraction ofmaterial weighted by the index of refraction of the material. By usingnanostructures with negative refractive index, localized pockets ofeffective medium with significantly different refractive index can beconstructed that have specific wavelength dependencies. In an idealcase, the effective index of refraction could be made to approach zeroor correspondingly the dielectric function c of the material canapproach zero for a specific range of wavelengths. This could beengineered to enhance outcoupling of a desired band of wavelengthsand/or suppress the outcoupling of undesired wavelengths. Thus, byvarying the metallic nanostructures fraction and shape, a color tuninglocal filter can be constructed which will also modify the line shape ofemission.

Examples

In some examples, inventors were able to tune the LSPR of a film ofmetallic nanostructures that are nearly spherical with a fixed diameter.The nanostructures are 5 nm in diameter and composed of Ag. Academicliterature typically refers to these as “colloidal metallicnanoparticles” or “Ag nanoparticles” and those terms apply here. Byvarying the thickness of the Ag nanoparticle film, inventors were ableto fine tune the LSPR over the spectral range relevant to blueorganometallic emissive materials. This tuning is a requirement toenable line shape engineering. FIGS. 3A and 3B illustrate systematictuning of the 5 nm Ag nanoparticle film and its line shape engineeringeffect on a blue organometallic complex. FIG. 3A is a normalized plotshowing the extinction spectrum of the LSPR of 5 nm Ag nanoparticlefilms of different thicknesses. Ag nanoparticle films having thicknesses15 nm, 28 nm, 60 nm, and 120 nm are represented. The corresponding peakextinction (absorption and scattering) wavelengths were 484 nm, 467 nm,448 nm, and 433 nm, respectively. The vertical line at 453 nm representsthe desired peak emission wavelength of the blue organometallic emissivecompound. Note here that the nanostructures are in electroniccommunication and that as the thickness of the Ag nanostructure filmincreases the peak extinction wavelength of the LSPR decreases as thecoupling between the nanoparticles increases and the material on thewhole looks more like bulk Ag. Thus, by allowing electroniccommunication between nanostructures we enable additional tuning of theLSPR via the number of layers of the nanostructures. If thenanostructures were prevented from electronic communication (as can beobtained by insulating the surface) then the LSPR would no longer be afunction of the thickness of the nanostructure film.

FIG. 3B shows emission spectra of blue organometallic phosphor placed inproximity to each of the Ag nanoparticle films of FIG. 3A. Surprisingly,the line shape of the emission spectrum of the blue organometallicphosphor changed with the change in the thickness of the Ag nanoparticlefilm. The intrinsic emission spectrum (a) of the blue organometallicphosphor (i.e., without any Ag nanoparticle film) exhibit an undesiredsecondary emission peak 10 that has a longer wavelength than the primaryemission peak 20 at 453 nm. The emission spectra (b), (c), (d), and (e)correspond to the effects of the LSPR from the Ag nanoparticle films of15 nm, 28 nm, 60 nm, and 120 nm thick, respectively. As can be seen, theemission spectrum (d), corresponding to the Ag nanoparticle filmthickness of 60 nm, exhibited the lowest secondary emission peak withoutaffecting the primary emission peak. This means that for this particularblue organometallic phosphor, a 60 nm thick Ag nanoparticle filmprovided in proximity to the emitter layer can be used to tune the lineshape of the phosphor's emission spectrum to maximize the peak emissionat the peak 20. It should be noted here that the nanoparticle films inproximity of an organometallic phosphor may also increase the totalemitted light from the organometallic phosphor.

This effect can be used to tune the peak emission wavelength of anorganometallic phosphor. FIG. 4 illustrates this schematically for ahypothetical organometallic phosphor. The peak wavelength of theemission spectrum 30 without a metallic nanostructure film is about 502nm. By providing an appropriate metallic nanostructure film in proximityto the emitter layer, one can change the line shape of the emissionspectrum of the emitter so that its peak is at 479 nm as illustrated bythe emission spectrum 40.

Combination with Other Materials

The materials described herein as useful for a particular layer in anorganic light emitting device may be used in combination with a widevariety of other materials present in the device. For example, emissivedopants disclosed herein may be used in conjunction with a wide varietyof hosts, transport layers, blocking layers, injection layers,electrodes and other layers that may be present. The materials describedor referred to below are non-limiting examples of materials that may beuseful in combination with the compounds disclosed herein, and one ofskill in the art can readily consult the literature to identify othermaterials that may be useful in combination.

Conductivity Dopants:

A charge transport layer can be doped with conductivity dopants tosubstantially alter its density of charge carriers, which will in turnalter its conductivity. The conductivity is increased by generatingcharge carriers in the matrix material, and depending on the type ofdopant, a change in the Fermi level of the semiconductor may also beachieved. Hole-transporting layer can be doped by p-type conductivitydopants and n-type conductivity dopants are used in theelectron-transporting layer.

Non-limiting examples of the conductivity dopants that may be used in anOLED in combination with materials disclosed herein are exemplifiedbelow together with references that disclose those materials:EP01617493, EP01968131, EP2020694, EP2684932, US20050139810,US20070160905, US20090167167, US2010288362, WO06081780, WO2009003455,WO2009008277, WO2009011327, WO2014009310, US2007252140, US2015060804 andUS2012146012.

HIL/HTL:

A hole injecting/transporting material to be used in the presentinvention is not particularly limited, and any compound may be used aslong as the compound is typically used as a hole injecting/transportingmaterial. Examples of the material include, but are not limited to: aphthalocyanine or porphyrin derivative; an aromatic amine derivative; anindolocarbazole derivative; a polymer containing fluorohydrocarbon; apolymer with conductivity dopants; a conducting polymer, such asPEDOT/PSS; a self-assembly monomer derived from compounds such asphosphonic acid and silane derivatives; a metal oxide derivative, suchas MoO_(x); a p-type semiconducting organic compound, such as1,4,5,8,9,12-Hexaazatriphenylenehexacarbonitrile; a metal complex, and across-linkable compounds.

EBL:

An electron blocking layer (EBL) may be used to reduce the number ofelectrons and/or excitons that leave the emissive layer. The presence ofsuch a blocking layer in a device may result in substantially higherefficiencies, and or longer lifetime, as compared to a similar devicelacking a blocking layer. Also, a blocking layer may be used to confineemission to a desired region of an OLED. In some embodiments, the EBLmaterial has a higher LUMO (closer to the vacuum level) and/or highertriplet energy than the emitter closest to the EBL interface. In someembodiments, the EBL material has a higher LUMO (closer to the vacuumlevel) and or higher triplet energy than one or more of the hostsclosest to the EBL interface. In one aspect, the compound used in EBLcontains the same molecule or the same functional groups used as one ofthe hosts described below.

Host:

The light emitting layer of the organic EL device of the presentinvention preferably contains at least a metal complex as light emittingmaterial, and may contain a host material using the metal complex as adopant material. Examples of the host material are not particularlylimited, and any metal complexes or organic compounds may be used aslong as the triplet energy of the host is larger than that of thedopant. Any host material may be used with any dopant so long as thetriplet criteria is satisfied.

Examples of metal complexes used as host are preferred to have thefollowing general formula:

wherein Met is a metal; (Y¹⁰³-Y¹⁰⁴) is a bidentate ligand, Y¹⁰³ and Y¹⁰⁴are independently selected from C, N, O, P, and S; L¹⁰¹ is an anotherligand; k′ is an integer value from 1 to the maximum number of ligandsthat may be attached to the metal; and k′+k″ is the maximum number ofligands that may be attached to the metal.

Emitter:

An emitter example is not particularly limited, and any compound may beused as long as the compound is typically used as an emitter material.Examples of suitable emitter materials include, but are not limited to,compounds which can produce emissions via phosphorescence, fluorescence,thermally activated delayed fluorescence, i.e., TADF (also referred toas E-type delayed fluorescence), triplet-triplet annihilation, orcombinations of these processes.

Non-limiting examples of the emitter materials that may be used in anOLED in combination with materials disclosed herein are exemplifiedbelow together with references that disclose those materials:CN103694277, CN1696137, EB01238981, EP01239526, EP01961743, EP1239526,EP1244155, EP1642951, EP1647554, EP1841834, EP1841834B, EP2062907,EP2730583, JP2012074444, JP2013110263, JP4478555, KR1020090133652,KR20120032054, KR20130043460, TW201332980, U.S. Ser. No. 06/699,599,U.S. Ser. No. 06/916,554, US20010019782, US20020034656, US20030068526,US20030072964, US20030138657, US20050123788, US20050244673,US2005123791, US2005260449, US20060008670, US20060065890, US20060127696,US20060134459, US20060134462, US20060202194, US20060251923,US20070034863, US20070087321, US20070103060, US20070111026,US20070190359, US20070231600, US2007034863, US2007104979, US2007104980,US2007138437, US2007224450, US2007278936, US20080020237, US20080233410,US20080261076, US20080297033, US200805851, US2008161567, US2008210930,US20090039776, US20090108737, US20090115322, US20090179555,US2009085476, US2009104472, US20100090591, US20100148663, US20100244004,US20100295032, US2010102716, US2010105902, US2010244004, US2010270916,US20110057559, US20110108822, US20110204333, US2011215710, US2011227049,US2011285275, US2012292601, US20130146848, US2013033172, US2013165653,US2013181190, US2013334521, US20140246656, US2014103305, U.S. Pat. No.6,303,238, U.S. Pat. No. 6,413,656, U.S. Pat. No. 6,653,654, U.S. Pat.No. 6,670,645, U.S. Pat. No. 6,687,266, U.S. Pat. No. 6,835,469, U.S.Pat. No. 6,921,915, U.S. Pat. No. 7,279,704, U.S. Pat. No. 7,332,232,U.S. Pat. No. 7,378,162, U.S. Pat. No. 7,534,505, U.S. Pat. No.7,675,228, U.S. Pat. No. 7,728,137, U.S. Pat. No. 7,740,957, U.S. Pat.No. 7,759,489, U.S. Pat. No. 7,951,947, U.S. Pat. No. 8,067,099, U.S.Pat. No. 8,592,586, U.S. Pat. No. 8,871,361, WO06081973, WO06121811,WO07018067, WO07108362, WO07115970, WO07115981, WO08035571,WO2002015645, WO2003040257, WO2005019373, WO2006056418, WO2008054584,WO2008078800, WO2008096609, WO2008101842, WO2009000673, WO2009050281,WO2009100991, WO2010028151, WO2010054731, WO2010086089, WO2010118029,WO2011044988, WO2011051404, WO2011107491, WO2012020327, WO2012163471,WO2013094620, WO2013107487, WO2013174471, WO2014007565, WO2014008982,WO2014023377, WO2014024131, WO2014031977, WO2014038456, WO2014112450,

HBL:

A hole blocking layer (HBL) may be used to reduce the number of holesand/or excitons that leave the emissive layer. The presence of such ablocking layer in a device may result in substantially higherefficiencies and/or longer lifetime as compared to a similar devicelacking a blocking layer. Also, a blocking layer may be used to confineemission to a desired region of an OLED. In some embodiments, the HBLmaterial has a lower HOMO (further from the vacuum level) and or highertriplet energy than the emitter closest to the HBL interface. In someembodiments, the HBL material has a lower HOMO (further from the vacuumlevel) and or higher triplet energy than one or more of the hostsclosest to the HBL interface.

In one aspect, compound used in HBL contains the same molecule or thesame functional groups used as host described above.

In another aspect, compound used in HBL contains at least one of thefollowing groups in the molecule:

wherein k is an integer from 1 to 20; L¹⁰¹ is an another ligand, k′ isan integer from 1 to 3.

ETL:

Electron transport layer (ETL) may include a material capable oftransporting electrons. Electron transport layer may be intrinsic(undoped), or doped. Doping may be used to enhance conductivity.Examples of the ETL material are not particularly limited, and any metalcomplexes or organic compounds may be used as long as they are typicallyused to transport electrons.

In one aspect, compound used in ETL contains at least one of thefollowing groups in the molecule:

wherein R¹⁰¹ is selected from the group consisting of hydrogen,deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy,aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl,aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile,isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinationsthereof, when it is aryl or heteroaryl, it has the similar definition asAr's mentioned above. Ar¹ to Ar³ has the similar definition as Ar'smentioned above. k is an integer from 1 to 20. X¹⁰¹ to X¹⁰⁸ is selectedfrom C (including CH) or N.

Charge Generation Layer (CGL)

In tandem or stacked OLEDs, the CGL plays an essential role in theperformance, which is composed of an n-doped layer and a p-doped layerfor injection of electrons and holes, respectively. Electrons and holesare supplied from the CGL and electrodes. The consumed electrons andholes in the CGL are refilled by the electrons and holes injected fromthe cathode and anode, respectively; then, the bipolar currents reach asteady state gradually. Typical CGL materials include n and pconductivity dopants used in the transport layers.

In any above-mentioned compounds used in each layer of the OLED device,the hydrogen atoms can be partially or fully deuterated. Thus, anyspecifically listed substituent, such as, without limitation, methyl,phenyl, pyridyl, etc. encompasses undeuterated, partially deuterated,and fully deuterated versions thereof. Similarly, classes ofsubstituents such as, without limitation, alkyl, aryl, cycloalkyl,heteroaryl, etc. also encompass undeuterated, partially deuterated, andfully deuterated versions thereof.

It is understood that the various embodiments described herein are byway of example only, and are not intended to limit the scope of theinvention. For example, many of the materials and structures describedherein may be substituted with other materials and structures withoutdeviating from the spirit of the invention. The present invention asclaimed may therefore include variations from the particular examplesand preferred embodiments described herein, as will be apparent to oneof skill in the art. It is understood that various theories as to whythe invention works are not intended to be limiting.

1. A method for engineering a line shape of emission spectrum of anorganic emissive material in an electroluminescent device, wherein theelectroluminescent device comprises an anode layer, a cathode layer, andan emissive layer disposed in between the anode and the cathode layers,wherein an organic emissive material is provided in the emissive layer,the method comprising: providing a layer of plasmonic metallicnanostructures having a localized surface plasmonic resonance (LSPR),wherein the layer of plasmonic metallic nanostructures is greater than 2nm from but less than 100 nm from the emissive layer and the LSPR of thelayer of plasmonic metallic nanostructures is within ±10 nm of the peakemission wavelength of the organic emissive material.
 2. The method ofclaim 1, wherein the LSPR of the layer of plasmonic metallicnanostructures is within ±5 nm of the peak emission wavelength of theorganic emissive material
 3. An electroluminescent device, comprising:an anode layer; a cathode layer: and a stack of layers disposed betweenthe anode layer and the cathode layer, said stack of layers including:an emissive layer comprising an organic emissive material, the organicemissive material having an emission wavelength; and a first layer ofplasmonic metal nanostructures having a localized surface plasmonicresonance (LSPR), wherein the layer of plasmonic metal nanostructures isat a distance greater than 2 nm from but less than 100 nm from theemissive layer and the LSPR of the layer of plasmonic metalnanostructures is tuned to be within ±10 nm of the peak emissionwavelength of the organic emissive material.
 4. The device of claim 3,wherein the LSPR of the layer of plasmonic metal nanostructures is tunedto be within ±5 nm of the peak emission wavelength of the organicemissive material.
 5. The device of claim 3, wherein the stack of layerscomprising a hole transporting layer (HTL) disposed between the emissivelayer and the anode layer, and wherein the first layer of plasmonicmetal nanostructures is disposed between the HTL and the anode layer. 6.The device of claim 5, wherein the first layer of plasmonic metalnanostructures has a thickness and the thickness is selected to resultin the LSPR of the first layer of plasmonic metal nanostructures bewithin ±10 nm of the peak emission wavelength of the organic emissivematerial.
 7. The device of claim 6, wherein the LSPR of the first layerof plasmonic metal nanostructures is within ±5 nm of the peak emissionwavelength of the organic emissive material.
 8. The device of claim 5,wherein the first layer of plasmonic metal nanostructures has athickness and comprises a plurality of plasmonic metal nanostructureshaving a particle size wherein the particle size is selected to resultin the LSPR of the first layer of plasmonic metal nanostructures iswithin ±10 nm of the peak emission wavelength of the organic emissivematerial.
 9. The device of claim 8, wherein the LSPR of the first layerof plasmonic metal nanostructures is within ±5 nm of the peak emissionwavelength of the organic emissive material.
 10. The device of claim 3,wherein the stack of layers comprising an electron transporting layer(ETL) disposed between the emissive layer and the cathode layer, whereinthe first layer of plasmonic metal nanostructures is disposed betweenthe ETL and the cathode layer.
 11. The device of claim 10, wherein thefirst layer of plasmonic metal nanostructures has a thickness and thethickness is selected to result in the LSPR of the first layer ofplasmonic metal nanostructures being within ±10 nm of the peak emissionwavelength of the organic emissive material.
 12. The device of claim 11,wherein the LSPR of the first layer of plasmonic metal nanostructures iswithin ±5 nm of the peak emission wavelength of the organic emissivematerial.
 13. The device of claim 10, wherein the first layer ofplasmonic metal nanostructuress has a thickness and comprises aplurality of plasmonic metal nanostructures having a particle size,wherein the particle size is selected to result in the LSPR of the firstlayer of plasmonic metal nanostructures being within ±10 nm of the peakemission wavelength of the organic emissive material.
 14. The device ofclaim 13, wherein the LSPR of the first layer of plasmonic metalnanostructures is within ±5 nm of the peak emission wavelength of theorganic emissive material.
 15. The device of claim 10, wherein the stackof layers further comprising a hole transport layer (HTL) disposedbetween the emissive layer and the anode layer, and wherein a secondlayer of plasmonic metal nanostructures is disposed between the HTL andthe anode layer.
 16. The device of claim 15, wherein each of the firstand second layers of plasmonic metal nanostructures has a thickness andthe thickness of each of the first and second layers of plasmonic metalnanostructures is selected to result in the LSPR of the first and secondlayers of plasmonic metal nanostructures being within ±10 nm of the peakemission wavelength of the organic emissive material.
 17. The device ofclaim 16, wherein the LSPR of the first and layers of plasmonic metalnanostructures is within ±5 nm of the peak emission wavelength of theorganic emissive material.
 18. The device of claim 15, wherein each ofthe first and second layers of plasmonic metal nanostructures has athickness and comprises a plurality of plasmonic metal nanostructureshaving a particle size, wherein the particle size of the plurality ofplasmonic metal nanostructures is selected to result in the LSPR of thefirst and second layers of plasmonic metal nanostructures being within±10 nm of the peak emission wavelength of the organic emissive material.19. The device of claim 18, wherein the LSPR of the first and secondlayers of plasmonic metal nanostructures is within ±5 nm of the peakemission wavelength of the organic emissive material.
 20. The device ofclaim 3, wherein the first layer of plasmonic metal nanostructures is apatterned plasmonic metal film, wherein the patterned plasmonic metalfilm has a feature size selected to result in the LSPR of the patternedplasmonic metal film be within ±10 nm of the peak emission wavelength ofthe organic emissive material.
 21. The device of claim 20, wherein theLSPR of the patterned plasmonic metal film is within ±5 nm of the peakemission wavelength of the organic emissive material.
 22. Anelectroluminescent device, comprising: an anode layer; a cathode layer:and a stack of layers disposed between the anode layer and the cathodelayer, said stack of layers including: an emissive layer comprising anorganic emissive material, the organic emissive material having anemission wavelength; a hole transporting layer disposed between theemissive layer and the anode layer; and an electron transporting layerdisposed between the emissive layer and the cathode; wherein (1) or (2)is true: (1) the anode layer or the cathode layer is a layer ofplasmonic metal nanostructures having a localized surface plasmonicresonance (LSPR), or (2) a layer of plasmonic metal nanostructureshaving a LSPR that is disposed either between the hole transportinglayer and the anode layer or between the electron transporting layer andthe cathode layer, wherein the layer of plasmonic metal nanostrcuturesis at a distance greater than 2 nm from but less than 100 nm from theemissive layer and the LSPR of the layer of plasmonic metalnanostructures is tuned to be within ±10 nm of the peak emissionwavelength of the organic emissive material.
 23. The device of claim 22,wherein the LSPR of the layer of plasmonic metal nanostructures iswithin ±5 nm of the peak emission wavelength of the organic emissivematerial.
 24. The device of claim 22, wherein the layer of plasmonicmetal nanostructures has a thickness and the thickness of the layer ofplasmonic metal nanostructures is selected to result in the LSPR of thelayer of plasmonic metal nanostructures is within ±10 nm of the peakemission wavelength of the organic emissive material.
 25. The device ofclaim 24, wherein the LSPR of the layer of plasmonic metalnanostructures is within ±5 nm of the peak emission wavelength of theorganic emissive material.
 26. The device of claim 22, wherein the layerof plasmonic metal nanostructures has a thickness and comprises aplurality of plasmonic metal nanostructures having a particle sizewherein the particle size is selected to result in the LSPR of the layerof plasmonic metal nanostructures be within ±10 nm of the peak emissionwavelength of the organic emissive material.
 27. The device of claim 26,wherein the LSPR of the layer of plasmonic metal nanostructures iswithin ±5 nm of the peak emission wavelength of the organic emissivematerial.
 28. The device of claim 22, wherein the layer of plasmonicmetal nanostructures is a patterned plasmonic metal film, wherein thepatterned plasmonic metal film has a feature size selected to result inthe LSPR of the patterned plasmonic metal film be within ±10 nm of thepeak emission wavelength of the organic emissive material.
 29. Thedevice of claim 28, wherein the LSPR of the patterned plasmonic metalfilm is within ±5 nm of the peak emission wavelength of the organicemissive material.